package org.bouncycastle.asn1.x509;

import org.bouncycastle.asn1.ASN1Encodable;
import org.bouncycastle.asn1.ASN1OctetString;
import org.bouncycastle.asn1.ASN1TaggedObject;
import org.bouncycastle.asn1.DERObject;
import org.bouncycastle.asn1.DEROctetString;
import org.bouncycastle.crypto.Digest;
import org.bouncycastle.crypto.digests.SHA1Digest;

/**
 * The SubjectKeyIdentifier object.
 * 
 * <pre>
 * SubjectKeyIdentifier::= OCTET STRING
 * </pre>
 */
public class SubjectKeyIdentifier extends ASN1Encodable {
    private byte[] keyidentifier;

    public static SubjectKeyIdentifier getInstance(ASN1TaggedObject obj,
            boolean explicit) {
        return getInstance(ASN1OctetString.getInstance(obj, explicit));
    }

    public static SubjectKeyIdentifier getInstance(Object obj) {
        if (obj instanceof SubjectKeyIdentifier) {
            return (SubjectKeyIdentifier) obj;
        }

        if (obj instanceof SubjectPublicKeyInfo) {
            return new SubjectKeyIdentifier((SubjectPublicKeyInfo) obj);
        }

        if (obj instanceof ASN1OctetString) {
            return new SubjectKeyIdentifier((ASN1OctetString) obj);
        }

        if (obj instanceof X509Extension) {
            return getInstance(X509Extension
                    .convertValueToObject((X509Extension) obj));
        }

        throw new IllegalArgumentException("Invalid SubjectKeyIdentifier: "
                + obj.getClass().getName());
    }

    public SubjectKeyIdentifier(byte[] keyid) {
        this.keyidentifier = keyid;
    }

    public SubjectKeyIdentifier(ASN1OctetString keyid) {
        this.keyidentifier = keyid.getOctets();
    }

    /**
     * Calculates the keyidentifier using a SHA1 hash over the BIT STRING from
     * SubjectPublicKeyInfo as defined in RFC3280.
     * 
     * @param spki
     *            the subject public key info.
     */
    public SubjectKeyIdentifier(SubjectPublicKeyInfo spki) {
        this.keyidentifier = getDigest(spki);
    }

    public byte[] getKeyIdentifier() {
        return keyidentifier;
    }

    public DERObject toASN1Object() {
        return new DEROctetString(keyidentifier);
    }

    /**
     * Return a RFC 3280 type 1 key identifier. As in:
     * 
     * <pre>
     * (1) The keyIdentifier is composed of the 160-bit SHA-1 hash of the
     * value of the BIT STRING subjectPublicKey (excluding the tag,
     * length, and number of unused bits).
     * </pre>
     * 
     * @param keyInfo
     *            the key info object containing the subjectPublicKey field.
     * @return the key identifier.
     */
    public static SubjectKeyIdentifier createSHA1KeyIdentifier(
            SubjectPublicKeyInfo keyInfo) {
        return new SubjectKeyIdentifier(keyInfo);
    }

    /**
     * Return a RFC 3280 type 2 key identifier. As in:
     * 
     * <pre>
     * (2) The keyIdentifier is composed of a four bit type field with
     * the value 0100 followed by the least significant 60 bits of the
     * SHA-1 hash of the value of the BIT STRING subjectPublicKey.
     * </pre>
     * 
     * @param keyInfo
     *            the key info object containing the subjectPublicKey field.
     * @return the key identifier.
     */
    public static SubjectKeyIdentifier createTruncatedSHA1KeyIdentifier(
            SubjectPublicKeyInfo keyInfo) {
        byte[] dig = getDigest(keyInfo);
        byte[] id = new byte[8];

        System.arraycopy(dig, dig.length - 8, id, 0, id.length);

        id[0] &= 0x0f;
        id[0] |= 0x40;

        return new SubjectKeyIdentifier(id);
    }

    private static byte[] getDigest(SubjectPublicKeyInfo spki) {
        Digest digest = new SHA1Digest();
        byte[] resBuf = new byte[digest.getDigestSize()];

        byte[] bytes = spki.getPublicKeyData().getBytes();
        digest.update(bytes, 0, bytes.length);
        digest.doFinal(resBuf, 0);
        return resBuf;
    }
}
